Diagnostic composition and test indicator



United States Patent M 3,266,868 DIAGNOSTIC COMPOSITION AND TEST INDICATOR Edward K. Harvill, Elkhart, Ind., assignor to Miles Laboratories, Inc., Elkhart, Ind., a corporation of Indiana No Drawing. Filed Jan. 24, 1962, Ser. No. 168,553 4 Claims. (Cl. 23253) This invention relates to a new and improved diagnostic composition and is particularly concerned with a diagnostic test which is useful for the qualitative detection and quantitative determination of glucose in biological fluids, such as urine, and wherein the reagent composition is incorporated upon a bibulous carrier.

The detection of glucose in urine as well as the determination of its concentration therein is of great importance for diabetic patients who must control their diets so as to regulate their sugar intake and who must frequently be guided in this regard by a regular check on urine glucose. But beyond its usefulness in regular urine testing on known diabetics by both patients and physicians, this glucose indicator may also be used efficiently in routine urinalyses in hospitals and physicians oflices, in diabetes screening programs, in the differentiation of glucosuria from other meliturias, and the like.

Because early diagnosis and continued control are so important in diabetes, a urine-sugar test, to be of greatest value, must be conveniently rapid, simple enough for any patient to learn with ease, accurate enough to serve the clinician, and sensitive enough to reflect variations in the patients condition. Moreover, the reagent composition must be adequately stable.

Procedures for the detection of sugar in urine are well known in clinical chemistry. One such procedure utilizes Benedicts copper reduction test, another employs a selfheating alkaline copper reduction test in tablet form (US. Patent No. 2,387,244), still another involves a test which depends solely on the action of enzymes (U.S. application No. 514,395, filed June 9, 1955, and now a'bandoned, by Alfred H. Free and assigned to the assignee of the present invention). These and other procedures have greatly contributed to the art of diagnosing for urine glucose.

It has been found that a unique combination of a glucose oxidase system for determining glucose with a novel indicator system using an iodide-molybdate accelerator for detecting hydrogen peroxide offers a superior means for testing biological fluids for their glucose content. This basic discovery is claimed in application Serial No. 813,336 now Patent No. 3,016,292, assigned to the instant assignee.

The diagnostic composition according to the basic invention described in the copending application just referred to comprises as essential constituents glucose oxidase, an iodide salt, such as potassium iodide, a molybdate salt, such as sodium molybdate, and a color-forming substance or indicator, such as 2,7-diaminofluorene.

The glucose oxidase (glucose aerodehydrogenase), as is well known, catalyzes the aerobic oxidation of glucose to produce gluconic acid (gluconolactone) and hydrogen peroxide. The iodide and molybdate salts, in turn, are capable of inducing the oxidation of the indicators by hydrogen peroxide formed in the oxidation of glucose.

Patented August 16, 1966 The latter reaction may be represented 'by the following schematic equation:

H10 Diaminofluorene (colorless) NazMoO;

Oxidized diamlnofluorene (blue color) The degree of blue color formation is immediately but accurately indicative of the glucose content of the fluid being tested.

The principle underlying the function of the iodide and molybdate salts as well as their coaction or interaction is not yet fully understood. However, it appears that, analytically, it is their role to serve as electron-transfer agents. It has been found that due to their collective presence-with one intensifying the effect of the other the reaction proceeds at a faster rate and lesser concentrations of hydrogen peroxide and, accordingly, glucose may be determined. These salts may therefore, be referred to as accelerators and promoters which hasten and enhance the oxidation of the indicator substance by hydrogen peroxide.

The incorporation-and use in this new glucose diagnostic of potassium iodide and sodium molybdate, both of which are corrunercially available, represents a substantial and significant advance in the art pertaining to glucose diagnostics. Glucose indicators in stick form presently on the market depend for the detection of hydrogen peroxide on the action of enzymes, such as peroxidases. The instant glucose indicator on the contrary, makes use of a non-enzymatic agent which permits a more accurately controllable and more definite composition. A very sensitive test for hydrogen peroxide and, accordingly, glucose, is thus made possible.

It has recently been found, however, that high levels of ketone substances in body fluids, such as acetoacetic acid in urine, have a tendency to interfere with the electron transfer reaction in some degree and in some measure reduce the sensitivity of the determination. For example, levels of acetoacetic acid above about mg. percent have been found to interfere slightly with the sensitivity of the test for glucose.

This interference has, in accordance with the instant invention, been eliminated by the present discovery. It has been found, and forms the object'of this invention, that an improved diagnostic composition for the detection of glucose which is not reduced in sensitivity by the presence of ketonic substances may be prepared by the incorporation of a metallic salt of a chelating agent into a formulation which contains a flavoprotein of glucose oxidase, an iodide salt, and a molybdate salt with a colorforming substance oxidizable by hydrogen peroxide in the presence of iodide and molybdate salts.

In place of the potassium iodide and sodium molybdate it is also possible, and therefore contemplated, to employ other equivalent iodide and molybdate salts. For example, other iodides, such as sodium and ammonium iodides and other molybdates, such as potassium and ammonium molybdates may also be used. As a colorforming substance, 2,7-diamino-fluorene, o-tolidine, odianisidine, leucoindophenols, etc., may be used.

From the detailed examples below it is evident that such additives as suitable rotective, thickening, wetting, suspending agents and the like are incorporated in the reagent composition as well as inert dyes to impart thereto a uniform color background.

Furthermore, it is important to include an appropriate buffer system to maintain a desired pH range in the presence of urine. Although the pH range may vary between 4 to 7.5, an especially preferred pH is 6.7.

Although the test device itself may comprise the reagent composition in the form of a tablet, powder or other embodiment, we prefer to aflix the reagent composition on bi'bulous base materials or carriers, such as strips or sticks of filter paper, by dissolving the components in a suitable solvent, impregnating the bibulous strips with the resulting solution, and drying the impregnated test strips. Embodying the diagnostic composition in the form of test sticks insures ease and simplicity of test procedure.

Set out in detail below is an example of the preparation of a diagnostic composition in accordance with the prior art:

EXAMPLE I Formula the impregnating solution Preparation for impregnating solution The following procedure was used in preparing the impregnating solution:

(1) Dissolve 250 mg. 2,7-diaminofluorene.2HCl and 500 mg. o-tolidine.HCl in ml. H O by heating. Complete solution does not occur, but when added to the PVA and when the alcohol is added a clear solution forms.

(2) Add ml. 15% PVA.

(3) Add 1 ml. tris-malonate buffer.

(4) Add ml. 95% alcohol.

(5) Add 14 ml. tris-malonate buffer.

(6) Add 10 ml. 5% gelatin.

(7) Dissolve 1.6 g. KI .and 1.0 g. Na MoO .2H O in 10 ml. water and add to above.

(8) Add 1 ml. 1% foam inhibitor.

(9) Add 2 ml. 3.5% FD & C Red #3 solution.

(10) Dissolve 1.5 g. glucose oxidase #3961 in 10 ml. water and add to the above.

Preparation of reagent strips Bibulous strips, such as filter paper cut into narrow strips, are dipped into the impregnating solution so that through the process of submersion and capillary attraction about one-half inch of the strip at one end is com pletely impregnated. These strips .are then dried in a drying tunnel or in a forced draft oven. The test portion of these strips is of a red color. It will be understood that other porous or absorbing materials, such as small sticks of wood, etc., and other methods of applying the impregnating solution and of drying the impregnated sticks may likewise be employed.

The test strips of this example are extraordinarily sensitive when compared to test strips commercially available but, as shown, their sensitivity is somewhat impaired by the presence of ketonic substances present in body fluids being tested.

TABLE I Mg. Percent Acetoacetie Acid Percent Glucose It will be seen that in' the presence of acetoacetic acid in amounts of about 160 mg. percent and above, the sensitivity of the prior .art tests was impaired.

In accordance with the instant inventive concept the formulation of the tests strips of Example I above was varied slightly by the incorporation into the formula of a heavy metallic salt of a chelating agent. This formulation is set out in detail in Example II as follows:

EXAMPLE II Formula of impregnating solution Metallic chelate (ferric salt of ethylene diamine Preparation of the impregnating solution The following procedure was used in preparing the impregnating solution:

(1) Dissolve 250 mg. 2,7-diaminofiuorene.2HCl and 500 mg. o-tolidine.HCl and l g. Sequestrene NaFe purified in 10 ml. H O by heating. Complete solution does not occur, but when added to the PVA and when the alcohol is added a clear solution forms.

(2) Add 15 ml. 15% PVA.

(3) Add 1 ml. tris-malonate buffer.

(4) Add 30 ml. alcohol.

(5) Add 14 m1. tris-malonate buffer.

(6) Add 10 ml. 5% gelatin.

(7) Dissolve 1.6 g. KI and 1.0 g. Na MoO .2H O in 10 ml. water and add to above.

(8) Add 1 ml. 1% Aerosol O-T.

(9) Add 2 ml. 3.5% FD & C Red #3 solution.

(10) Dissolve 1.5 g. glucose oxidase #3961 in 10 ml. water and add to the above.

Preparation of reagent strips Reagent strips were prepared as described in connection with Example I above.

The improved reagent strips of Example II were tested against the same urines as set out in Table I above with the following results:

TABLE II Mg. Percent Acetoacetic Acid Percent Glucose 0.1 L L L L- L-- 0.25 11+ L L- L L- 0.50 M- L L L- L 1.0. M L L L L 2.0 M L+ L L L 4.0. M+ M- L L L 6. M M- L L L It will be seen that the improved composition of this invention completely eliminates the impaired sensitivity experienced with the strips of the prior art.

EXAMPLE III Using the basic formula set out in Example I above, various amounts of several levels of the ferric salt of EDTA were incorporated into the formulation, as follows:

(a) 300 mg. of the iron ohelate (b) 400 mg. of the iron chelate (c) 500 mg. of the iron chelate (d) 750 mg. of the iron chelate CHzCOONa CHzC 00 where Fe represents the metal and is selected from the group consisting of copper, nickel, manganese and iron, with iron being especially preferred.

In the examples given above the molybdate salt used is the sodium salt and the iodide salt selected is the potassium salt. It is to be understood, of course, that other salts may be used. For example, operable molybdate salts include sodium and potassium. Sodium and ammonium iodide may be used as the iodide salts.

Set out below is a table of the operable and preferred ranges of proportions of the major constituents of the compositions of the instant invention:

To summarize briefly, the present invention relates to a diagnostic test for the detection of glucose in body fluids, especially in urine, which is not sensitive to interference by ketonic substances. The improved composition of the instant invention, consists of a bibulous material which has been impregnated with a composition comprising glucose oxidase, an iodide salt, a molybdate salt, an oxidizable substance which changes color in the presence of hydrogen peroxide and said salts and a metallic salt of a chelating agent. The preferred embodiment of the present invention comprises a bibulous material which has been impregnated with a composition consisting of glucose oxidase, potassium iodide, sodium molyb-date, 2,7-diaminofluorene, and an iron salt of ethylene diamine tetraaeetic acid.

What is claimed is:

1. A diagnostic composition for detecting glucose which comprises glucose oxidase, an iodide salt selected from the group consisting of potassium iodide, sodium iodide, and ammonium iodide, a molybdate salt selected from the group. consisting of sodium molybdate, potassium molybdate, and ammonium molybdate, a color-forming substance oxidizable by hydrogen peroxide in the presence of said iodide and molybdate salts, and a metallic salt of a chelating agent selected from the group consisting of the copper, nickel, manganese and iron salts of ethylene diamine tetra-acetic acid.

2. A diagnostic composition for detecting glucose which com-prises glucose oxidase, an iodide salt selected from the group consisting of potassium iodide, sodium iodide, and ammonium iodide, a molybdate salt selected from the group consisting of sodium molybdate, potassium molybd'ate, and ammonium molybdate, a color-forming substance selected from the group consisting of 2,7-diaminofluorene, o-tolidine, and dianisidine and mixtures thereof, and a metallic salt of a chel-ating agent selected from the group consisting of the copper, iron, nickel and manganese salts of ethylene diamine tetraacetic acid.

3. A diagnostic composition for detecting glucose which comprises glucose oxidase, potassium iodide, sodium molybdate, 2,7-diaminoiiuorene, o-tolidine and the ferric salt of ethylene diamine tetraacetic acid.

4. A test indicator for detecting glucose which comprises a bibulous material which contains therein the dried residue resulting from deposition on said material, followed by drying, of a liquid comprising glucose oxidase, potassium iodide, sodium molybdate, 2,7-diaminofluorene, o-tolidine, and the ferric salt of ethylene diamine tetraacetic acid.

References Cited by the Examiner UNITED STATES PATENTS 2,848,308 8/1958 Free 23-230 2,981,606 4/1961 Keston 23-230 2,982,700 5/1961 Adams 23-230 2,990,253 6/1961 Smeby 23-253 2,990,338 6/1961 Gibson 23-230 3,016,292 1/1962 Bauer et -al 23-253 3,042,496 7/1962 Fancher et al 23-253 3,104,209 9/1963 Scott 252-408 X 3,123,443 3/1964 Smeby -1035 X 3,143,476 8/1964 Grant 167-87.1

MORRIS O. WOLK, Primary Examiner.

ANTHONY SCIAMANNA, Examiner. 

4. A TEST INDICATOR FOR DETECTING GLUCOSE WHICH COMPRISES A BIBULOUS MATERIAL WHICH CONTAINS THEREIN THE DRIED RESIDUE RESULTING FROM DEPOSITION ON SAID MATERIAL, FOLLOWED BY DRYING, OF A LIQUID COMPRISING GLUCOSE OXIDASE, POTASSIUM IODIDE, SODIUM MOLYBDATE, 2,7-DIAMINOFLUORENE, O-TOLIDINE, AND THE FERRIC SALT OF ETHYLENE DIAMINE TETRAACETIC ACID. 